1. Field of the Invention
The present invention relates to an optical receiver and an optical network system using thereof, particularly to an optical receiver preferably used for a star-type optical network such as an optical subscriber system and a station-side apparatus of the star-type optical network.
2. Description of the Related Art
A PON (Passive Optical Network) system is known as means for economically realizing an optical subscriber system, which is disclosed in the official gazette of Japanese Patent Laid-Open No. 61-30139. The PON system aims at economization by connecting optical transceivers 121 and 131 in one station side 100 with optical transceivers 221 to 22N and 231 to 23N in a plurality of subscriber-sides 201 to 20N by single-mode fibers 301 to 30N through a passive splitter 141 and thereby, sharing one station-side optical transceiver by a plurality of subscribers as shown in FIG. 5.
However, a lot of branch loss due to a passive splitter 141 and deterioration of the reception sensitivity of an up receiving section related to optical burst transmission for time-division multiple access cause the number of branches to be extremely restricted or the price of a subscriber-side optical transceiver for obtaining a required number of branches to rise.
In FIG. 5, symbols 110 and 211 to 21N denote access control sections and 241 to 24N denote optical couplers.
As means for effecting a system at less allowable loss between transmission and reception sides while making the best use of the access control system of the PON, the following are known instead of a passive splitter: passive multiplexing using a single-mode multi-mode combiner, passive multiplexing of leading the light emitted from a plurality of single fibers to a large-aperture photoelectric converter element by using a lens, and passive multiplexing of connecting a plurality of single-mode fibers with an array photoelectric converter element constituted with a plurality of photoelectric converter element and receiving the output light current of the array photoelectric converter element by one electronic circuit. These arts are described in xe2x80x9cPDS constitution method reducing confluent loss of up signalxe2x80x9d (p. 621) in the lecture number B-10-112 in the general meeting of IEICE (Institute of Electronics, Information, and Communication Engineers) in 1997.
Particularly, the passive multiplexing using the array photoelectric converter element shown in FIG. 6 is prospective because expensive optical parts such as a single-mode multi-mode combiner and a large-aperture lens coupling system are unnecessary.
The structure of a passive-multiplexing optical receiver using a conventional array photoelectric converter element is described below by referring to FIG. 6.
The optical receiver is a burst receiver in which amplitudes of a receiving-circuit input signal current are suddenly changed every reception packet, which uses a differential amplifier 20 at the initial stage of the receiving circuit similarly to the case of the burst receiving circuit disclosed in the official gazette of Japanese Patent Laid-Open No. 2-266630 or described in the lecture number C-501 of the society general meeting of IEICE.
Signal rays emitted from optical fibers 11 to 18 of an eight-core-ribbon optical fiber cable 10 are led to photoelectric converter planes of an 8-channel photodiode array 0 and photoelectrically converted. The photodiode array 0 is formed on a semi-insulating substrate and anode and cathode terminals are output from photoelectric converter elements 1 to 8 forming an array. Anodes of the photoelectric converter elements 1 to 8 are connected in common and connected to a positive-phase input terminal 21 of the differential amplifier 20 and cathodes of the elements 1 to 8 are connected in common and connected to a reverse-bias applying positive power supply VCC.
Moreover, a dummy capacitor 9 having a capacitance almost equal to a parasitic capacitance added to the positive-phase input terminal 21 due to mounting a photodiode on that terminal 21 are connected to the negative-phase input terminal 22 of the differential amplifier 20.
When an optical signal is output from any one of the optical fibers 11 to 18, a photo current enters the positive-phase input terminal 21 of the differential amplifier 20, the potential of a positive-phase output terminal 23 rises, and the potential of a negative-phase output terminal 24 lowers. Thus, passive multiplexing is realized by using an array photoelectric converter element.
The output of the differential amplifier 20 is discriminated between two values of logics xe2x80x9c1xe2x80x9d and xe2x80x9c0xe2x80x9d by a discrimination circuit 40 by passing through a discrimination-level control circuit 30 corresponding to a burst signal and is output.
However, the optical receiver using the conventional array photoelectric converter element shown in FIG. 6 has disadvantages that the junction capacitance of the element increases because a lot of photoelectric converter elements are connected in parallel and causes a response speed to deteriorate and noises to increase.
It is an object of the present invention to constitute an optical receiver having a small junction capacitance between photoelectric converter elements, that is, a high-speed low-noise optical receiver used for passive multiplexing of a time-division multiple-access optical transmission system.
It is another object of the present invention to inexpensively realize extension of a time-division multiple-access optical transmission system or increase of the number of systems to be accommodated, which is very useful.
An optical receiver of the present invention includes a differential input amplifier, a first photoelectric converter element whose cathode is connected to a reverse-bias power supply and whose anode is connected to one input terminal of the differential input amplifier, and a second photoelectric converter element whose anode is connected to a reverse-bias power supply and whose cathode is connected to the other input terminal of the differential input amplifier.
Moreover, the first photoelectric converter element comprises a plurality of photoelectric converter element groups whose cathodes are connected in common and whose anodes are connected in common and the second photoelectric converter element comprises a plurality of photoelectric converter element groups whose cathodes are connected in common and whose anodes are connected in common.
Moreover, at least one of a photoelectric converter element group comprising a plurality of the first photoelectric converter elements, a photoelectric converter element group comprising a plurality of the second photoelectric converter elements, and a photoelectric converter element group comprising the first and second photoelectric converter elements is integrated in a semiconductor substrate.
Furthermore, the differential input amplifier is a transimpedance amplifier returned from a negative-phase output to a positive-phase input and from a positive-phase output to a negative-phase input respectively through a circuit element including a resistance element.
Furthermore, the differential input amplifier includes a first transimpedance amplifier having an input terminal serving as the above one input terminal and a second transimpedance amplifier having an input terminal serving as the above other input terminal and having the same structure as the first transimpedance amplifier, and a differential amplifier using the outputs of the first and second transimpedance amplifiers as differential inputs.
An optical network system of the present invention includes a master station having the above optical receiver, a slave station having an optical transmitter, and an optical fiber for connecting the optical receiver of the master station with the optical transmitter of the slave station.
Moreover, the optical receiver of the master station and the optical transmitter of the slave station are controlled by a time-division multiple-access control circuit.
Functions of the present invention are described below. Photoelectric converter elements constituting a photodiode array are divided into two groups. A reverse bias is applied to cathodes of one group and anodes of the group are connected to one input of a differential input amplifier. A reverse bias is applied to anodes of the other group and cathodes of the group are connected to the other input of the differential input amplifier.
Thus, the number of photoelectric converter elements connected to the input end of the differential input amplifier is halved and thereby, the junction capacitances of the photoelectric converter elements are halved. Therefore, the operation speed of the optical receiver is increased and noises of the optical receiver are reduced. Because noises of the optical receiver are reduced, and a time-division multiple-access optical transmission system is extended or the number of systems to be accommodated is increased by using the optical receiver.